This invention relates to an apparatus and a method for detecting a communication channel in whose frequency band radio signals from different radio signals inside a cabin, in particular inside an aircraft cabin of an aircraft, are simultaneously transmitted.
Aircrafts are provided with a speak intercom or on-board communication system by means of which members of the aircraft crew are able to inform passengers or can issue instructions regarding the behaviour of passengers.
Airlines are also increasingly offering passengers the possibility of communicating via W-LAN (Wireless Local Area Network) or other wireless transmission technologies, for example. A passenger can use his mobile terminal device, e.g. a laptop, to exchange data with a local network of the aircraft via a wireless interface. In this case the data are transmitted in a communication channel whose frequency band lies in a frequency range which is determined by the relevant transmission technology. The wireless communication systems transmit data in licensed and unlicensed frequency bands. A licensed frequency band allows excessive access to a predetermined range of the frequency spectrum, wire ranges of the licensed spectrum being allocated to specific transmission technologies, e.g. GSM or UMTS.
Unlicensed frequency bands are available to all users for signal transmission, but the permissible transmission signal power is limited. The so-called ISM bands (Industrial, Scientific and Medical Band) represent an example of license-free frequency bands for license-free audio and video transmission or for data transmission in W-LAN or Bluetooth. Another example of an unlicensed frequency band is represented by the U-NII frequency band (Unlicensed National Information Infrastructure Band) at approx. 5 GHz.
In conventional transmission systems for wireless data transmission with mobile terminal devices of air passengers, it may transpire that because of a non-optimised configuration, in terms of frequency band allocation, a plurality of users are able to transmit data simultaneously in communication channels which use the same frequency band Δf. Consequently the data transmission rate for the users concerned is reduced and this may result in increased bit error rates due to interference.
Another disadvantage of a conventional communication system for transmitting data inside an aircraft cabin of an aircraft lies in the fact that previously a separate on-board communication system had to be provided to guarantee, in any situation, that the crew members are able to give instructions to the passengers. In the conventional on-board communication system a crew member, for example the stewardess or the pilot, speaks into a microphone which is fixedly connected to the on-board communication system. The travelling passengers hear the instructions or information over speakers which are installed inside the aircraft cabin. One disadvantage of a conventional on-board communication system consists in the fact that a crew members, for example a stewardess, is only able to make an announcement to the passengers when she has reached the permanently wired terminal device of the on-board communication system and there speaks into a microphone of a receiver. However, reaching the on-board communication system is difficult for the crew member in certain flight situations.
An object of the invention is therefore to provide a device and method which allows wireless communication of crew members between each other and with the passengers without infringing the requirements regarding flight safety.